1. Field of the Invention
This invention is directed to an insulating wall structure for application to an existing wall structure, especially to wood-frame construction.
2. Description of the Prior Art
There is a need to better thermally insulate the exterior wall structures of existing buildings in these times of diminishing and ever more costly energy resources. The escalation of energy costs in recent years has been accompanied by increased concern on the part of home owners, builders and utility companies for economical, high efficiency thermal insulation systems, particularly for wood frame residential construction. One increasingly accepted insulation system developed to meet this need involves an exterior retrofitting method, i.e., the residing of an existing wall structure, with a thermal insulating material being disposed between the existing and new siding.
One problem which can arise from the application of this type of retrofit insulation to existing frame walls is that, where the insulation applied is impermeable, it may promote moisture accumulation within the existing or old section of the retrofitted composite. On the other hand, where the new insulation is permeable, there is also the possibility that under severe winter conditions it may also promote moisture or frost and ice accumulation in the new retrofit section of the composite wall. Either situation could result in the risk of premature deterioration.
One prior art method of moisture relief involves cold air wash venting in which a positive air flow is provided by installing a ventilating structure at both the top and bottom of the wall. This method is thermally inadequate since it introduces cold outside air to the "warm" side of the retrofitted insulation material, thus negating the insulating value provided by the retrofitted insulation material.
In U.S. Pat. No. 4,129,972 there is disclosed an insulating wall system for new construction in which heat flow through a wall is inhibited by thermal insulation materials within two spaced moisture- and air-impermeable barriers. A cold air wash is prevented in this wall structure by means of a moisture- and air-impermeable seal at its bottom. Only the top of the structure is kept open to permit the relief of what little moisture might enter therein. The novel wall system disclosed in U.S. Pat. No. 4,129,972 can thus be likened to a large dimensional bottle in which only the top has an uninsulated opening while the rest of the bottle is substantially resistant to heat and moisture flow. While this disclosed wall structure serves to increase the insulating efficiency of the opaque walls of new buildings and to limit moisture entry into these walls, it is not necessarily designed for application to existing buildings where the existing opaque walls may already be established with lesser degrees of moisture and air permeability. Furthermore, total reconstruction of existing walls in accordance with the patent would not be a realistic economic option.